The present invention relates to a control valve for use in a variable displacement compressor.
Generally, vehicle air conditioners include a condenser, an expansion valve, as a depressurizing device, an evaporator, and a compressor. The compressor draws refrigerant gas from the evaporator, compresses it, and then discharges the compressed gas to the condenser. The evaporator transfers heat between the refrigerant flowing in the refrigerant circuit and air in the vehicle. In accordance with the cooling load, the heat of air passing near the evaporator is transferred to the refrigerant flowing in the evaporator. The pressure of the refrigerant gas in the vicinity of the outlet of the evaporator reflects the cooling load.
A swash plate type variable displacement compressor for such an air conditioner is provided with a displacement control system for steering the pressure (suction pressure Ps) near the outlet of the evaporator to a predetermined suction pressure. The displacement control system controls the discharge displacement of the compressor, i.e., the inclination angle of its swash plate, to obtain a flow rate corresponding to the cooling load.
In the control process, a pressure sensing member such as a bellows or a diaphragm, senses the suction pressure Ps. In accordance with the displacement of the pressure sensing member, the valve opening is controlled to regulate the pressure in a crank chamber (crank pressure Pc).
A simple control valve that imposes a single target suction pressure cannot control the air conditioning performance accurately. Therefore, an electromagnetic control valve that changes the target suction pressure in accordance with an external current has been proposed. Such a control valve includes an actuator such as a solenoid. A force acting on the sensing member is changed in accordance with the current to the actuator. Accordingly, the target suction pressure is adjusted.
According to the above-described control method, however, even if the target suction pressure is changed by electric control, the actual suction pressure may not reach the target suction pressure. That is, the cooling load is likely to affect whether or not the actual suction pressure responds well to changes in the target suction pressure. It is not therefore possible to promptly and reliably alter the displacement of a compressor even if the actual suction pressure is regulated as needed by electric control.
It is an object of the present invention to provide a control valve for a variable displacement compressor that changes the displacement of the compressor quickly and reliably.
To achieve the above objective, the present invention provides a control valve used for a variable displacement compressor in a refrigerant circuit. The compressor changes the displacement in accordance with the pressure in a crank chamber and includes a supply passage, which connects a discharge pressure zone to the crank chamber, and a bleed passage, which connects a suction pressure zone to the crank chamber. The control valve comprises a valve housing. A valve chamber is defined in the valve housing. The valve chamber is part of the supply passage or the bleed passage. A movable valve body is located in the valve chamber. The valve body adjusts an opening size of the supply passage or the bleed passage in the valve chamber. A valve body regulator regulates the movement of the valve body. A first urging member urges the valve body towards the valve body regulator. A sensing chamber is defined in the valve housing. A sensing member is located in the sensing chamber to divide the sensing chamber into a first pressure chamber and a second pressure chamber. The sensing member engages with and disengages from the valve body. The pressure of a first pressure monitoring point located in the refrigerant circuit is applied to the first pressure chamber. The pressure of a second pressure monitoring point located in the refrigerant circuit is applied to the second pressure chamber. The sensing member moves in accordance with the pressure difference between the first pressure chamber and the second pressure chamber. A sensing member regulator regulates the movement of the sensing member. The sensing member regulator is located in the second pressure chamber. A temporary chamber is formed between the sensing member and the valve body when the valve body is disconnected from the sensing member. The temporary chamber is connected to the second pressure chamber. A second urging member urges the sensing member toward the sensing member regulator. An actuator applies a force to the valve body that is opposite to the force of the first urging member and that of the second urging member in accordance with commands from an external controller. The actuator changes a target pressure difference, which is a reference value for the operation of the sensing member.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.